Contact sensing probes generally include a first, fixed part connected to a machine which supports the fixed part for movement relative to a workpiece to be measured. The probe includes a movable part, having a stylus which is intended to engage the workpiece. Support means are provided to support the movable part in a rest position on the fixed part and the movable part is displaced from the rest position when the stylus engages the workpiece. Sensing means are provided for sensing such engagement and for producing a signal to be sent to a measuring system on the machine for determining the position of the fixed part.
A contact sensing probe is known in which the contact of a stylus with a workpiece is sensed by a piezo-electric sensor and an electric circuit is provided to produce said signal from the output of the piezo-electric sensor. Examples are shown in the UK Pat. Specifications Nos. 1,586,052 and 2,049,198, and in our co-pending International Patent Application published as No. WO 86/03829.
The known probes offer increased sensitivity over probes which sense physical displacement of the stylus since they can produce a signal triggered by initial contact of the stylus with the workpiece.